Here we would like to derive the constraint on coefficient \({\cal G}_1\)  by directly using the posterior samples obtained in [1]} for testing the amplitude birefringent effect with 12 LIGO-Virgo O1/O2 events. The data for all the 12 GW events are downloaded in [2]}. In [1]}, the amplitude birefringent effect due to parity violation is described by a parameter \(A_\nu \) , which can be related to \({\cal G}_1\)  in the spatial covariant gravity via
\(\delta h_1 = - A_\nu \pi f = - \left.\frac{1}{2} \frac{{\cal G}_1 k}{a}\right|^{a_0}_{a_e}.\) 
